Thermal treated reinforcing bar splice and method

ABSTRACT

A reinforcing bar has a controlled heating on its threaded end (or other engagement portion for engaging a coupler), which extends beyond the threads, and provides improved mechanical properties at the end. The heating may be a controlled heating that case hardens the threaded end, including heating of an unthreaded portion beyond the threaded portion. The heating may be done in multiple steps, for example with a heating/hardening, follow by cooling, a reheating for tempering, and a recooling. The bar end may be threaded into a coupler or splice, with the heated end extending axially beyond (outside of) the coupler. Regions of the reinforcing bar beyond the heated end may be untreated, and therefore weaker than the thermally-treated bar end. The resulting coupling or splice may therefore be able to achieve bar break (failure at a location in the bulk of the bar, away from the coupler).

This application claims priority under 35 USC 119 to U.S. Provisional Application 61/667,465, filed Jul. 3, 2012, which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is in the field of reinforcing bar splices, and machines and methods involving such reinforcing bar splices.

2. Description of the Related Art

In its simplest form, a mechanical rebar splice couples two pieces of rebar together by cutting tapered threads onto the male rebar ends, which are threaded into each half of the female sides of the coupler. Taper threads are preferred because of the ease of assembly requiring only a few turns of the sleeve coupler or rebar and the ability to avoid cross threading and subsequent damage to the threads. For headed rebar applications, only one piece of rebar is threaded into the coupler.

The threading process rolls or cuts the tapered threads in the rebar end including the nominal diameter and any projecting ribs or deformations. The process however notches the rebar and such couplings will not consistently achieve rebar break tensile capacity required by the higher performance code body requirements.

Different methods have been applied in achieving rebar break remote using a tapered (or straight) thread, coupler design. Swaging or cold forming the rebar end prior to threading is a method used to increase the tensile properties at the threaded area of the rebar. This swaging method is evidenced by U.S. Pat. No. 6,880,224 held by ERICO. The swaging is accomplished solely by radial compression and in the process flattens or deforms any radially projecting ribs or ridges on the rebar end. After the radial compression, the rebar end section is then formed with tapered or straight threads by cutting or rolling.

Several issues are possible with the swaging method. First, cold working the material requires a number of different die sets to accommodate a range of rebar sizes. These die sets must work with portable, auxiliary equipment designed to be used in the field. There are limitations with equipment such as clamping tonnage on larger rebar due to the portability of the equipment. Second, as the outside diameter of rebar increases, the cold working has less effect on tensile performance given the limitation of clamping tonnage of the swaging equipment. Third, stress concentrations due to rib geometry are inherent to rebar and is out of the control of the coupler manufacturer. There are many different rib patterns and further cold working of the ribs can increase notch sensitivity. Finally, in the event the rebar breaks outside the coupler, the swaging method does not control the location of bar break. Code body standards require the rebar breaks a set distance from the outside face of the coupler.

Upsetting the rebar end is another common practice. Manufacturers will upset the rebar end to obtain a larger diameter end section, which then receives a tapered or straight thread which has a larger average pitch diameter than the nominal diameter of the rebar. This method is evidenced in the following U.S. Pat. Nos. 5,709,121, 5,660,594, 5,158,527, 5,152,118, and 4,619,096

Issues also arise with the upsetting method. First, the forging process is conducive to leaving residual stresses in the upset geometry. These stresses can lead to failure within the coupler. Second, upsetting the material requires an increase in the overall stock diameter of the coupler and/or multiple components used in the coupler assembly, which may result in a cost prohibitive solution. Third, forging rebars with multiple types of rib patterns can lead to inconsistent final geometry of the rebar end. These inconsistencies require secondary operations such as hand grinding of the rebar end, resulting in further processing, equipment, and cost. Finally, the forging and/or secondary operations may lead to repeatability and/or reproducibility issues if not properly controlled. Further, inconsistent rebar end geometry can result in failure to meet code body performance requirements other than bar break remote, such as slip compliance.

In view of the shortcomings of prior methods of achieving bar break, improved methods would be desirable.

SUMMARY OF THE INVENTION

According to aspects of the invention, a reinforcing bar splice includes: a reinforcing bar with a threaded end; and a sleeve with internal threads that the threaded end is threaded into; wherein the threaded end is thermally treated. The splice may include one or more of the following features: the threaded end is thermally treated using induction heating; the threaded end is part of a thermally-treated section that extends beyond the threaded end; a portion of the thermally-treated section that extends beyond the threaded end may share some or all of the characteristics of the threaded end; the thermal treatment removes residual stresses in ribs in at least part of the reinforcing bar, such as in the portion of the thermally-treated section that extends beyond the threaded end; the thermal treatment normalizes material of the reinforcing bar due to rib deformations; provides consistent microstructure throughout the processed bar end; the thermally-treated section is a localized section that does not extend along the entire reinforcing bar; the thermally-treated section extends for a length of at least two bar diameters beyond a limit of threads of the threaded end; the thermally-treated section extends for a length of approximately two bar diameters beyond a limit of threads of the threaded end; the threaded end has tapered threads; the threaded end has straight threads; the thermal treatment of the threaded end case hardens the threaded end; the thermal treatment of the threaded end through hardens the threaded end; the thermal treatment of the threaded end increases strength of threads of the threaded end, which aids in preventing the threads from stripping when loaded; the thermal treatment improves microstructure of the threaded end; the thermal treatment improves wear resistance of the threaded end; the characteristics of the threaded end that are affected (or effected) by the thermal treatment are substantially the same about a circumference of the threaded end; the thermal treatment does not substantially affect characteristics of a core of the threaded end; a portion of the core of the threaded end remains ductile; the threaded end has a hardened case and a ductile core; the threaded end has a hardened case and a hardened core; threads of the threaded end are formed by cutting; threads of the threaded end are formed by rolling; threads of the threaded end are formed by forging; the thermal treatment removes residual stresses induced by the thread-forming process (such as cutting or rolling to form the threads); a portion of the reinforcing bar is also swaged; a portion of the reinforcing bar is also cold worked; the threaded end is an upset bar end; the splice achieves bar break; the bar break is at least beyond the face of the sleeve; the sleeve is made from hex stock; the sleeve is made from round stock; internal threads of the sleeve are longer than the threaded end; the reinforcing bar is a first reinforcing bar, and including a second reinforcing bar as part of the splice, with the reinforcing bars engaging opposite ends of the sleeve; the second reinforcing bar may have any or all of the characteristics described above for the first reinforcing bar; the second reinforcing bar may be substantially identical to the first reinforcing bar; the second reinforcing bar may have different thermal treatment than the first reinforcing bar, vary for instance, in one or more of temperature, duration, heat load, cooling, quenching, and tempering.

According to other aspects of the invention, a reinforcing bar has an end of the reinforcing bar to engage a sleeve or coupler that is a thermally-treated end. The reinforcing bar has one or more of the following features; the thermally-treated end is a threaded end; the thermally-treated end is a threadless end; the threadless end is an upset threadless end; one or more of the reinforcing bar features described in the previous paragraphs.

According to yet other aspects of the invention, a method of producing a reinforcing bar end includes: heating an end of the reinforcing bar; and subsequent to the heating, cooling the reinforcing bar end. The method may include one or more of the following features: prior or subsequent to the heating, threading at least part of the end; the threading includes threading only part of the end, leaving an unthreaded portion of the end that is heated during the heating; the threading includes tapered threading; the threading includes straight-thread threading; the heating includes induction heating; the induction heating includes induction heating from a heating coil that surrounds the end; the heating includes substantially-uniform circumferential heating; the heating includes heating from a heater (heating device) that surrounds the bar end; the heating includes one or more of flame hardening, diffusion hardening, differential hardening, oven/furnace heating, and exothermic reaction; the heating does not affect characteristics of a core of the reinforcing bar end; the heating also affects characteristics of a core of the reinforcing bar end; the heating hardens both a case and all or part of the core of the threaded end; the cooling includes quenching the bar end; the cooling includes bringing a quenchant, such as oil, water or another suitable liquid, into contact with the bar end; the cooling includes cooling using a cooler cooling device that surrounds the bar end; the method produces one or more of the reinforcing bar features described in the prior two paragraphs.

According to still other aspects of the invention, a device for treating an end of a reinforcing bar includes: a heater for heating the end; and a cooler for cooling the end. The device may include one or more of the following features: the heater surrounds the bar end; the heater is an induction heater; the induction heater is a coil; the heater provides substantially uniform heating to a surface of the bar end; the cooler includes a quencher; the quencher brings the bar end into contact with a quenchant, such as oil; the quencher brings the bar end into contact with a quenchant, such as water; the cooler surrounds the bar end; the heater and the cooler are aligned such that the reinforcing bar can pass through one of the heater and the cooler to reach the other; the device includes equipment, such as a controller, for controller the heater and/or the cooler; the device produces the reinforcing bar having any of the features of the first two paragraphs of this summary; the device is used in the method having any of the features of the last paragraph.

According to another aspect of the invention, a method of producing a reinforcing bar includes: threading a threaded end portion of the reinforcing bar; subsequent to the threading, heating a heated end of the reinforcing bar, wherein the heated end includes the threaded end portion of the reinforcing bar, and an unthreaded portion of the reinforcing bar beyond the threaded end portion; and subsequent to the heating, cooling the heated end of the reinforcing bar.

According to yet another aspect of the invention, a reinforcing bar splice includes: a reinforcing bar with a threaded end; and a sleeve with internal threads that the threaded end is threaded into; wherein a thermally-treated section of the reinforcing bar is thermally treated, with the thermally-treated section including the threaded end, and an unthreaded portion of the reinforcing bar that is outside of the sleeve.

According to a further aspect of the invention, a method of preparing a reinforcing bar includes the steps of: preparing an engagement portion of the reinforcing bar for mechanically engagement with a coupler to be mechanically coupled to the engagement portion; subsequent to the preparing, heating a heated end of the reinforcing bar, wherein the heated end extends beyond the engagement portion, and wherein a bulk of the reinforcing bar beyond the heated end is left unheated by the heating; and subsequent to the heating, cooling the heated end.

According to a still further aspect of the invention, a reinforcing bar splice includes: a reinforcing bar with an engagement portion at an end of the reinforcing bar; and a sleeve that mechanically engages the engagement portion to hold the engagement portion within the sleeve. A thermally-treated section of the reinforcing bar is thermally treated, with the thermally-treated section including the engagement portion, but not a bulk of the reinforcing bar beyond the thermally treated portion, and with the thermally-treated section outside of the sleeve.

According to another aspect of the invention, a reinforcing bar splice includes: a reinforcing bar with an engagement portion; and a sleeve that mechanically engages the engagement portion to hold the engagement portion within the sleeve. A strengthened end of the reinforcing bar is stronger than a bulk of the reinforcing bar beyond the strengthened end, with the strengthened end extending outside of the sleeve. The strengthened end includes a thermally-treated section that includes the engagement portion.

According to still another aspect of the invention, a method of preparing a reinforcing bar includes: preparing an engagement portion of the reinforcing bar for mechanically engaging another object; and substantially axisymmetrically heating a heated end of the reinforcing bar, wherein the heated end extends beyond the engagement portion, and wherein a bulk of the reinforcing bar beyond the heated end is left unheated by the heating.

To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The annexed drawings, which are not necessarily to scale, show various aspects of the invention.

FIG. 1 is an exploded side view, partially in cross section, of a reinforcing bar splice in accordance with an embodiment of the present invention.

FIG. 2 is a side view of part of a process of treating a rebar end of one of the reinforcing bars of FIG. 1.

FIG. 3 is a side view of another part of the process of treating the rebar end.

FIG. 4 is a flow chart of some steps of the method or process of treating a rebar end.

FIG. 5 is a side exploded view of a reinforcing bar splice system, in accordance with another embodiment of the invention.

FIG. 6 is a side exploded view of a reinforcing bar splice system, in accordance with still another embodiment of the invention.

FIG. 7 is a side, partially cross-sectional view of a reinforcing bar splice system, in accordance with yet another embodiment of the invention

DETAILED DESCRIPTION

A reinforcing bar has a controlled heating on its threaded end (or other engagement portion for engaging a coupler), which may extend beyond the threads, and provides improved mechanical properties at the end. The heating may be a controlled heating that case hardens the threaded end, including heating of an unthreaded portion beyond the threaded portion. The heating may be done in multiple steps, for example with a heating/hardening, follow by cooling, a reheating for tempering, and a recooling. The bar end may be threaded into a coupler or splice, with the heated end extending axially beyond (outside of) the coupler. Regions of the reinforcing bar beyond the heated end may be untreated, and therefore weaker than the thermally-treated bar end. The resulting coupling or splice may therefore be able to achieve bar break (failure at a location in the bulk of the bar, away from the coupler).

A rebar splice and method uses neither swaging nor upsetting to achieve bar break remote performance. It employs a combination of processes to achieve a unique, consistent rebar splicing system to overcome the common issues found in swaging and upsetting techniques. According to one embodiment, the process is the following: 1) the end(s) of the rebar is threaded (tapered or straight) to match the corresponding female thread(s) of the coupler sleeve; 2) a localized section of the rebar end is thermally treated using auxiliary power equipment, such as heating equipment, for example heating equipment or other equipment that allows control of input parameters such as coil positioning relative to the bar end, heating time, temperature, quenching and tempering times to control output parameters such as microstructure, hardness, case depth, and case profile along the length of the rebar end(s); and 3) the rebar end(s) is then threaded into the coupler end(s).

The term “end,” as used herein with regard to rebars, is meant to indicate a portion of the rebar in the vicinity of an axial end or terminus of the rebar. It is not meant to require that the “end” necessarily encompass that terminus (for example, the “end” may exclude an end face and a short length of bar adjacent to the end face.

As an alternative, the threading may be done after the localized section of the rebar is thermally treated. Also, the thermal treatment may be accomplished in any of a variety of suitable alternative processes.

Induction heating or other thermal treatment of the rebar results in a case hardened or through hardened rebar end. The case hardening yields important benefits. It provides increased strength to the threads, which will prevent the rebar threads from stripping when loaded.

While the case hardness provides a hardened, wear resistant improved microstructure surface, the mechanical properties of the rebar core is unaffected by the induction heating process or other heating process. This combination of a hardened case and ductile core results in a threaded rebar end with good strength and toughness characteristics.

The induction heating or other heating process removes any residual stresses from the rib pattern of the rebar by thermally treating the rebar ends. It further provides a consistent microstructure in the bar end. The length of the effective case extends past the threads of rebar end. This allows the rebar to be strengthened at any set distance from the face of the coupler. Further, it allows a minimum controlled location of where the rebar will break relative to the coupler. Thermal treatment of rebar ends to improve thread strength, resistance to notch sensitivity, and overall rebar splicing system performance.

The treatment method may allow control of the location of rebar break, for example to at least a minimum set distance outside the coupler face. The method may also relieve residual stresses and normalize rebar material due to rib deformations, for example providing consistent microstructure in the rebar material due to rib deformations. Further it may overcome dimensional instability of rebar.

With reference to FIGS. 1 and 2, the thermal-treated splicing system 20 includes reinforcing bars (rebars) 1 and 2, joined together by an internally-threaded sleeve or coupler 3. While the rebars 1 and 2 shown are of the same size, they can vary in rebar size by use of well known transition couplers with different size threads in each end matching that of the rebars. Further, for headed rebar applications, only one piece of rebar is threaded into the coupler.

Typically, the rebars 1 and 2 are deformed during the rolling process, and are provided with longitudinal diametrically opposite long ribs 4 and 5 on opposite sides of the rebars 1 and 2. The rebars 1 and 2 also include circumferential ribs 6 that are somewhat offset from circumferential ribs 7 on the opposite side. It should be noted that commercially available reinforcing bar may be provided with a wide variety of rib or deformation patterns. For more details of the various rebar deformations available, reference may be had to various publications of the Concrete Reinforcing Steel Institute (CRSI) of Chicago, Ill., USA.

The rebars 1 and 2 have a thermally treated in section 8, with an axial length A, which includes a threaded tip or end section 9 (having an axial length C) and an unthreaded thermally treated, cylindrical section 10 (having an axial length B). In the illustration embodiment shown in FIG. 1, the ribs 4-7 are not shown as extending into section 10, but it will be appreciated that the ribs 4-7 alternatively may extend into section 10. It is preferable that the axial length A of the thermally treated section 8 be longer than, and perhaps substantially longer than, the threaded length C, so that the ends or faces of the coupler 3, shown at 11 and 12 will be within (will overlap) the thermally treated area 9 and 10. When the coupler is assembled the faces 11 and 12 will be substantially at the inner end of the thread sections 9, leaving at least the distance B of thermally-treated material extending beyond the faces 11 and 12 of the coupler 3. The length B of the extending thermally treated section is approximately at a distance of two times the rebar diameter D, for example being between 1.5 and 2.5 times the diameter D, or between 0 and 2.5 times the diameter D, to give non-limiting ranges.

The sleeve 3 may be formed from hex or round stock, and has internal threads at each end shown at 13 and 14, which are configured to engage the matching taper threads of the rebar end section 9/10. The internal tapered threads in the sleeve 3 are slightly longer than the external threads on the tapered rebar end but the sleeve may be assembled quickly to the bar ends with relatively few turns and correct torque.

After the rebar end 9 is threaded, but prior to assembly with the sleeve 3, the end is thermally treated, for example via induction heating equipment. FIGS. 2 and 3 show a heating system 40, an example of a heater for treating rebar ends, such as the ends of rebars 1 and 2. FIG. 4 shows a flow chart of a method 60 for treating a rebar end.

In step 62, a predetermined length of the end 9/10 of the bar 1 is placed inside a round induction coil 42, which rapidly heats the threaded end 9. The coil 42 may be coupled to a suitable electrical power system (not shown), having for example suitable controls usable to provide a variable level of power for variable heating. The induction coil 42 may be protected by a safety shield 44, for example a series of annular members 46. The safety shield 44 may protect the coil 42 from damage, and users from contact with the hot coil 42. The power and frequency of electricity provided to the coil 42 may be selected to achieve a desired amount of heating to the bar end 9/10, for example an amount of heating used to achieve a desired case hardening of the bar end 9/10, while still allowing a soft core in the rebar regions 9 and 10. The bar ends 9 and 10 may be heated to a temperature of 820-1090° C. (1500-2000° F.), for a time of 1-30 seconds, using a heater power 50-300 kW, applying power at a frequency of 3-75 kHz. These values (and the other numerical values provided herein) are only example ranges, and are not meant to be limiting.

The inside of the induction coil 42 may be 1/30th bar diameter to two full bar diameter larger than outside diameter of the bar 1. The edge of the induction coil 42 may be position up to three bar diameters beyond the end of the rebar 1 in either direction. This is done to ensure that the magnetic flux density is correctly focused on the bar end. These are general ranges, and should not be considered limiting.

The induction coil 42 may advantageously provide controlled, substantially axisymmetric heat treatment of the bar end 9/10. The rebar 1 may be inserted into the coil 42 with the axes of the bar 1 and the coil 42 substantially aligned, so that the heating is applied substantially axisymmetrically.

After the heating process is completed, the rebar end 9 is cooled in step 64. The rebar end 9/10 may be moved to a quenching area, where the heated rebar end 9/10 is cooled by quenching, for example by bringing a quenchant, such as oil or another suitable liquid, into contact with the heated rebar end, for example by spraying, submersing, or another suitable process. Quenchant temperature can range from 10-150° C. (50-300° F.).

After the initial quenching in step 64, the rebar end 9/10 may be heated again, in a tempering process (step 66). The rebar end 9/10 may again be place in the induction coil 42 for heating. In the tempering process the heating may be a lower level than in the heating/hardening of step 62. For example, may be heated to a temperature of 150-540° C. (300-1000° F.), for a time of 5-60 seconds, using a heater power 1-100 kW, applying power at a frequency of 1-65 kHz. The electrical power provided to the induction coil 62 may be reduced, and/or there may be a change in the frequency of the power provided. With the lower power provided to the heater, the amount of the rebar end 9 heated at any one time (the length of rebar end heated) may be reduced, relative to the heating in step 62. Therefore during some or all of the tempering in step 66 the rebar 1 may be moved relative to the induction coil 42. This may be accomplished by any of a variety of suitable mechanisms, for example with the rebar 1 moved manually or by use of a suitable motor. This movement can be actuated by piston, ball screw, or other mechanical means. The ability to adjust position of the rebar 1 relative to the heater 40 allows for achievement of uniform mechanical properties in the heated rebar regions 9 and 10. The tempering process of step 66 may be applied to the same parts of the rebar 1 as the original heating (the end regions 9 and 10). The tempering improves the toughness of the end regions while retaining most of the strength and hardness created in step 62. The resulting hardness values in step 66 are reduced 1-40% from those attained in step 62.

Finally, following the tempering in step 66, in step 68 the rebar end 66 is again cooled. This may be accomplished by suitable quenching, or other suitable cooling methods as discussed above with regard to step 64.

In the illustrated embodiment the heating device (the induction coil) and the cooling device (the quenching station) are both coaxial about parts of the rebar, but many other arrangements are possible. The equipment controls input parameters such as coil positioning relative to the bar end, heating time, energy frequency, quenching and tempering times, to control output parameters such as microstructure, hardness, case depth, and case profile along the length of the rebar end(s).

Induction heating is only one example of a heating method in which the entire circumference of the bar end is heated simultaneously, for example with substantially uniform heating around the circumference. Other sorts of cooling than quenching may be used in alternative. The equipment or device may include additional features, such as manual or automatic timers, temperature or heating level controls, cooling controls, and/or mechanisms for moving the rebar.

The method described above advantageously provides a faster, controlled heating solution that provides even heating, in contrast to heating methods like a manual flame operation to heat the bar. In addition thermal treatment of the forged end removes any residual stresses left by the threading, rolling, or forging process. Further, induction heating (or other controlled heating methods) could be used on any swaged or cold worked of the bar to stress relieve a localized section of the bar. Finally, induction heating can be used to quickly heat the bar end prior to any forging or upsetting of the bar end.

The described embodiment involves a tapered bar end. However, alternatives in the bar end geometry are permissible in this system such as straight threads, threaded upset bar ends, threadless upset bar ends, etc.

The described embodiment involves induction heating equipment as its source of thermal treatment. Alternative heat treating methods and equipment may be used to achieve the same result of a localized thermally treated bar end. Such methods could include, but are not limited to, flame hardening, diffusion hardening, differential hardening, oven/furnace heating, exothermic reaction, etc.

By hardening the threaded and unthreaded portions of the rebar ends 9 and 10 the ends may be made stronger, and the failure of the spliced rebar coupling 20 may be moved away from the rebar ends and the sleeve or coupler 3. The bulk of the rebars 1 and 2 remains untreated, and these untreated portions serve as the points where failure will occur. Since the coupler 3 overlaps the heated (e.g., hardened/tempered) rebar ends 9 and 10, the coupler 3 and the associated bar ends are stronger than the untreated portions of the bar. Thus bar break is achieved, with failure occurring well away from the splice.

The discussion above is focused on a tapered thread reinforcing bar end. A tapered thread is only one example of an engagement portion at the end of a reinforcing bar, for mechanically engaging a splice or coupler, such as by being inserted in some way into the splice or coupler. FIG. 5 shows one alternative engagement portion, a straight-threaded engagement 80 on reinforcing bars 81 and 82, for engaging a suitable internally-threaded coupler or splice 84 as part of a splice system 86. The threads of the engagement 80 may be forged, for example.

FIG. 6 shows another alternative, an engagement portion that is a forged or upset end portion 90, on reinforcing bars 91 and 92, for placement in a suitable cavity of a splice or coupler 93, which includes a pair of parts 94 and 95 that thread together. The bars 91 and 92, and the coupler 93, together constitute a splice system 96. The heat treatments for the engagements 80 and 90 may be similar to those described above for the tapered thread engagement portion, with the heat treatment extending beyond the engagement portions 80 and 90, and outside of the couplers or splices 84 and 93, for example about two bar diameters beyond the limits of the couplers or splices.

FIG. 7 shows a further alternative, a splice system 100 in which reinforcing bars 101 and 102 have engagement portions 103 and 104 for engaging a splice or coupler 106. The engagement portions 103 and 104 are parts of strengthened ends having lengths 109 and 110, with bulk (unstrengthened or untreated) parts of the bars 101 and 102 beyond the strengthened ends 109 and 110. The strengthened ends 109 and 110 may include both heat-treated portions 111 and 112, and cold-worked portions 113 and 114 that extend beyond the heated-treated portions 111 and 112. The heat-treated portions 111 and 112 may include the engagement portions 103 and 104, and one or both of the engagement portions 103 and 104 may be fully within the splice or coupler 106. The cold-worked portions 113 and 114 may be the parts of the strengthened ends 109 and 110 that extend beyond the splice or coupler 106. The heat treatment of the heat-treated portions 111 and 112 may be similar to that described above for other embodiments. The cold working may be any suitable cold working process for strengthening the reinforcing bars 101 and 102 in the cold-worked portions 113 and 114. Although the engagement portions 103 and 104 are shown in FIG. 7 as upset or forged engagement ends, alternatively the engagement portions may be other types of engagement ends, for example straight or tapered threaded ends.

Many alternatives are possible. For example, the cold working may be omitted, with the strengthened portions being only the heat-treated portions, one or both of which may be fully within the splice or coupler 106 (not extending beyond the ends of the splice or coupler 106). The engagement portions in such a variation may be threaded or upset/forged. The heat treating, for instance axisymmetric heat treating as described above, may strengthen the reinforcing bar such that bar break occurs in the bulk of the bar, such as away from (outside of) the splice or coupler 106.

Another alternative is that a forged or upset end portion, for example the end portion 90 of the reinforcing bar 91 (FIG. 6), may itself be used as an anchor for engagement with a concrete or other structural member, without use of coupler or splice. The heat treatment may be an axisymmetric heat treatment, as described above, and may extend for 0 to 2.5 bar diameters beyond the upset end portion, for example. As a further alternative, a threaded bar end that engages an internally-threaded coupling or bar termination that acts as an anchor (as in the ERICO LENTON TERMINATOR system) may be heat treated (as described above) to strengthen the bar end, and such heat treatment may strengthen the bar beyond to coupling. The coupling (bar termination) may be a cylindrical mass or knob that has a diameter significantly greater than that of the reinforcing bar, so as to act as an anchor in concrete or other structure.

Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application. 

What is claimed is:
 1. A method of preparing a reinforcing bar, the method comprising: preparing an engagement portion of the reinforcing bar for mechanically engagement with a coupler to be mechanically coupled to the engagement portion; subsequent to the preparing, heating a heated end of the reinforcing bar, wherein the heated end extends beyond the engagement portion, and wherein a bulk of the reinforcing bar beyond the heated end is left unheated by the heating; and subsequent to the heating, cooling the heated end.
 2. The method of claim 1, wherein the heating includes induction heating the heated end, using a heater that surrounds at least part of the heated end.
 3. The method of claim 1, wherein the heating includes case hardening of the heated end, such that an outer part of the heated end is harder than an internal core of the heated end, which remains ductile.
 4. The method of claim 1, wherein the heating makes the heated end stronger than the bulk of the reinforcing bar.
 5. The method of claim 1, wherein the heating includes heating such that the heated end has an axial length of between 1.5 and 2.5 times a diameter of the engagement portion.
 6. The method of claim 1, wherein the cooling includes cooling the heated end using a liquid.
 7. The method of claim 1, further comprising, subsequent to the cooling, reheating at least part of the heated end.
 8. The method of claim 7, wherein the reheating is tempering of the at least part of the heated bar end.
 9. The method of claim 7, wherein the reheating is performed at a lower heating level then the heating.
 10. The method of claim 7, wherein reheating is accomplished using a heater that is also used in the heating.
 11. The method of claim 10, wherein the reinforcing bar is moved relative to the heater during the reheating.
 12. The method of claim 7, further comprising, after the reheating, recooling the heated bar end.
 13. The method of claim 1, wherein the preparing includes forming threads on the engagement portion.
 14. The method of claim 13, wherein the forming threads includes taper threading to form tapered threads.
 15. The method of claim 13, wherein the method is part of a method of making a reinforcing bar splice that includes threading the threads into an internally-threaded sleeve; and wherein, after the threading is completed, the heated end extends outside of the sleeve.
 16. The method of claim 1, wherein the method is part of a method of making a reinforcing bar splice that includes mechanically coupling the engagement portion with a coupler; and wherein, after the threading is completed, the heated end extends outside of the coupler.
 17. A reinforcing bar splice comprises: a reinforcing bar with an engagement portion; and a sleeve that mechanically engages the engagement portion to hold the engagement portion within the sleeve; wherein a strengthened end of the reinforcing bar is stronger than a bulk of the reinforcing bar beyond the strengthened end, with the strengthened end extending outside of the sleeve; and wherein the strengthened end includes a thermally-treated section that includes the engagement portion.
 18. The reinforcing bar splice of claim 17, wherein the engagement portion is a threaded portion that engages internal threads of the sleeve.
 19. The reinforcing bar splice of claim 17, wherein part of the strengthened end is a cold-worked section that is not part of the thermally-treated section.
 20. A method of preparing a reinforcing bar, the method comprising: preparing an engagement portion of the reinforcing bar for mechanically engaging another object; and substantially axisymmetrically heating a heated end of the reinforcing bar, wherein the heated end extends beyond the engagement portion, and wherein a bulk of the reinforcing bar beyond the heated end is left unheated by the heating. 